The present invention relates to an operation method and an operation control device for a servo press line in which a servo press and a servo transfer device are alternately disposed in the workpiece transfer direction.
A servo press line in which a servo press and a servo transfer device are alternately disposed in the workpiece transfer direction has been known. For example, a servo press line illustrated in FIG. 12 has a configuration in which a servo transfer device 30 is disposed between servo presses 10U and 10D. In FIG. 12, a first servo transfer device disposed on the upstream side of the left (first) servo press 10U is omitted.
Each of the servo presses 10U and 10D includes a slide 12, an upper die 13, a lower die 17, a bolster 18, and the like, and can perform a press operation. The servo transfer device 30 includes a main body 31, a carrier 32, and an adsorbing section 33, and can perform a transfer operation. In FIG. 13, the servo transfer device 30 disposed between the servo presses is illustrated at the center.
In FIGS. 12 and 13, a workpiece 35 transferred from the first servo transfer device to the first (left) servo press 10U (refer to a transfer step Tr3 (=Tr31+Tr32) in FIG. 13) is placed on the lower die 17 of the servo press 10U, and subjected to first press. The workpiece 35 subjected to first press is transferred to a neutral position Z by the second servo transfer device 30 disposed on the downstream side in the transfer direction (disposed between the presses 10U and 10D in FIG. 12) (transfer step Tr2 (=Tr21+Tr22) in FIG. 13), transferred to the servo press 10D (transfer step Tr3 (=Tr31+Tr32) in FIG. 13), and placed on the lower die 17 of the downstream-side servo press 10D.
The second servo transfer device 30 is moved from the second servo press 10D to the neutral position Z in an empty state (transfer step Tr4 (=Tr41+Tr42) in FIG. 13), and moved to the upstream-side servo press 10U in an empty state for the subsequent transfer cycle (transfer step Tr1 (=Tr11+Tr12) in FIG. 13). The servo transfer device 30 thus performs a normal transfer operation. The workpiece 35 is sequentially transferred to the downstream side by each servo transfer device 30, and subjected to given press by each servo press 10 to obtain a product.
The servo press line operation control method is classified as a master-slave method and an integral control method in the same manner as other industrial machines.
The master-slave method causes a slave press to follow a master press so that a difference in speed between the presses does not occur. For example, JP-A-2000-343294 discloses a method that causes the press speed of each press to follow the press speed of the first press (synchronous operation). The master-slave method relatively improves productivity as compared with a press line in which a press having a clutch-brake is disposed (i.e., the slide is temporarily stopped at the top dead center position corresponding to one rotation of the crank shaft). However, when a problem (e.g., a decrease in speed) occurs in the master press, the problem also occurs in each slave press.
In a servo press line using the integral control method, each servo press is integrally controlled. As illustrated in FIG. 12, a host controller 60P issues press instructions to each press controller 25P of each servo press 10, for example. Likewise, the host controller 60P issues transfer instructions to each transfer controller 55P of each servo transfer device 30. A display operation section 70P includes a display section 71 and an operation section 72.
In the press line in which the slide is temporarily stopped at the top dead center position, the press speed of the master press is reduced to a large extent in order to prevent a breakage of an expensive die. However, since the productivity decreases when reducing the press speed, this method cannot be directly employed for the servo press line using the integral control method. Specifically, the master-slave method cannot ensure the advantage (free slide motion) of the servo press.
For example, JP-A-2003-191096 discloses a servo press line in which the press speed of each servo press need not be reduced over the entire steps. This press line is formed so that each press is equally handled. The slide speed of each servo press is adjusted to the slide speed of one servo press (e.g., a servo press having the lowest slide speed) until the slide position reaches the workpiece transfer allowable position, and each slide position can reach the workpiece transfer allowable position at the same time. Therefore, the productivity can be improved while preventing interference.
As a servo press line that aims at further improving productivity, JP-A-2006-130560 discloses a servo press line in which an instruction value that quickens (or delays) the movement of the slide is output to the servo press that is determined to be delayed (or advanced) as compared with a reference press step (slide movement) so that the slide movement of each servo press is adjusted to (synchronized with) the reference slide movement.
However, the servo press line disclosed in JP-A-2006-130560 performs synchronization control between the servo presses having a relatively high speed in the same manner as the servo press line disclosed in JP-A-2003-191096, but does not perform synchronization control with the servo transfer device having a relatively low speed. Specifically, interference cannot be prevented by these technologies.
In order to prevent interference while maximizing press productivity, it is desirable to perform a normal transfer operation while setting the servo transfer device having a relatively low speed at the allowable highest transfer speed. The normal press operation is performed while setting the press speed of the servo press having a relatively high speed at a value lower than the allowable highest press speed within a range corresponding to the allowable highest transfer speed. This normal press operation method has been widely used along with the development of hardware and software.
However, the servo characteristics may change to some extent. A change in servo characteristics does not occur every cycle, but occurs due to accidents. A change in servo characteristics of the servo press occurs due to a change in load (press load), failure, or the like. A change in servo characteristics of the servo transfer device occurs due to a change in workpiece weight or mechanical friction, failure, or the like. In either case, the servo characteristics change to the low-speed side as compared with the set operation speed. The servo characteristics do not change to the high-speed side for the above-mentioned reasons.
A change in operation speed affects the productivity to only a small extent, and may be canceled within a short time (e.g., until the subsequent cycle starts). However, since interference occurs due to the relative positional relationship instead of the temporal relationship, it is necessary to deal with such a change in operation speed.